Powder coatings, especially epoxy powder coatings, are an extremely important category of energy-saving and low-pollution coatings. As early as 1952, Erwin Gemmer of Kriesheine, Germany, invented the fluidized bed dip coating method, which developed thermoplastic powder coatings; in 1962, the French Sames company developed electrostatic powder coating equipment, and in 1964, thermosetting powder coatings were successfully developed; In the 1980s, industrial waste gas, wastewater, and waste residues caused serious pollution to the environment. European and American countries have issued regulations on the restriction of volatile organic compounds (VOC). Especially after the United Nations Conference on Environment and Development in 1992, environmental protection has become a worldwide important question. So far, powder coating has attracted much attention because of its solvent-free, pollution-free, thick coating at one time, and the recyclability of oversprayed powder, and its development speed is very fast. At the same time, the utilization rate of powder coating is close to 100%, and the powder after spraying can be recycled; it is usually easier to construct than liquid coating, the formed coating film has good durability and significant product advantages. The automobile manufacturing industry is one of the largest users of coatings. Since the 1980s, developed countries have established strict control indicators for the emission of organic solvents in automobile production. From the VOC emissions of 15.5 pounds per vehicle in the late 1970s to 1.5 pounds per vehicle in the 21st century. In the past 20 years, each significant drop in emissions was related to the use of new coatings, such as the introduction of high-solid coatings in the early 1980s, water-based coatings in the late 1980s, and powder coatings in the 1990s.
Powder coatings have been used in automotive coatings for more than 20 years. However, automotive coatings require high weather resistance, high corrosion resistance, high wear resistance, heat resistance, gloss retention, color retention and other high performance and require excellent decoration. It is difficult to develop and research, and it is difficult to make breakthrough progress in a short period of time. The powder coating made of pure polyester resin also has characteristics: the coating film has good weather resistance and is suitable for the coating of outdoor products; the coating film has good heat resistance, and the coating film is not easy to yellow during baking and curing; the coating film is resistant Excellent physical properties such as impact strength, flexibility and hardness, good chemical resistance and water resistance; good coating performance, can be coated by air spraying and electrostatic powder coating; TGIC cured polyester powder coating , There is basically no reaction by-products during the baking and curing process, and the coating film is not prone to shrinkage, pinholes and other defects. Powder coatings are widely used in automotive topcoats and car body primers. Today's powder coatings can bring high-quality surfaces, and can form a strong bond with metal parts without primer coating. At the same time, powder coating It has excellent corrosion resistance, heat resistance, impact resistance and abrasion resistance, and a wide range of colors, including high-gloss, low-gloss, metallic or transparent coatings. The texture can be selected from smooth surface to wrinkled or rough coating. The thickness of the coating film can also be changed to suit different requirements. The performance of these powder coatings shows the maturity of today's powder coatings.
For a long time in the past, automobile assembly plants used liquid coatings. For most parts of the world, the use of powder coatings in automobile assembly plants is still an unsolved problem, although the past few years have been Great progress, but it has not yet reached the level of large-scale use of powder coatings. In the United States, the amount of powder coatings used in car topcoats and car body primers is the largest. Cars use powder primers to achieve good results, but powder coatings are used for car tops. The progress of the paint is not great, especially even less used as a car gloss finish. Some businesses believe that there is still a lot of room for powder coating to be used as a finishing coat, but the investment cost incurred by the switch to powder coating equipment in automobile factories makes it difficult to make up your mind. As the automobile industry pays more and more attention to the durability of automobiles, and powder coatings are not only more economical, but also have better corrosion resistance and destructiveness, so the use of powder coatings to coat automobile chassis and bodywork will become more and more widespread. my country started to use powder coatings for the coating of auto parts earlier. FAW had built a powder spraying assembly line as early as the 1990s, and other auto companies also carried out powder spraying of parts through outsourcing during the same period. Restricted by the variety, quality, technology and other factors of powder coatings, the variety and structure of powder coatings in my country is not conducive to automotive coatings. Automotive coatings require high weather resistance, and the majority of powder coatings in my country are epoxy/polyester. There are not many products of mixed powder and epoxy powder, improved epoxy powder, polyurethane powder, TGIC polyester powder, and acrylic powder suitable for outdoor use, and there are still many problems in quality.
Automobile powder coating preparation technology is progressing faster and faster. Traditional powder coatings including epoxy resin powder coating preparation methods are divided into dry method and wet method, and dry method is divided into dry mixing method and melt mixing method: wet method is divided into evaporation method , Spray drying method and precipitation method. In recent years, Ferro has developed a supercritical fluid method called VAMP (Vedoc Advanced Manufacturing Process). At present, the production of powder coatings mostly uses the melt mixing method. The disadvantages are that it is difficult to change varieties and colors, and the particle size distribution is relatively wide. It is difficult to produce low-temperature curing and ultra-fine particle size powder coatings. For this reason, people have improved the powder coating preparation process and made certain progress. The development and utilization of the supercritical fluid method is called a revolution in the preparation of powder coatings and will play an important role in the development of automotive powder coatings in the 21st century. The working principle of the supercritical fluid method is: carbon dioxide is liquefied when it reaches the critical point, and the interface between liquid carbon dioxide and gaseous carbon dioxide is clear. If the pressure drops slightly or the temperature is slightly higher, it will exceed the critical point, and this interface will disappear immediately. A piece of chaos is called the supercritical point. Continue to increase the temperature or decrease the pressure, and carbon dioxide becomes a gas. Using this principle, the powder raw materials are added to the supercritical liquid processing equipment with a stirring device, and the supercritical carbon dioxide fluidizes the components of the coating, so that the melt extrusion effect can be achieved at low temperatures. The materials are sprayed and granulated in the classifying kettle to obtain the product. The whole production process can be controlled by computer. The new VAMP process developed by Ferro in the United States is suitable for processing automotive powder coatings.
Its advantages are: the fully enclosed VAMP system avoids the pollution of dust and fibers in the surrounding environment and affects the cleanliness of the powder coating; the shape of the particles can be controlled, and the prepared powder coating has excellent friction and charging performance, so that the powder is During the spraying process, it can penetrate into hard-to-reach parts, the coating film thickness is uniform, and a thinner coating film can be obtained; the processing temperature is low to prevent the oxidation of the GMA acrylic resin and prevent the coating film from yellowing; the pre-reaction can be minimized. Conducive to powder flow and leveling, with good reproducibility; conducive to the processing of low-temperature curing powder coatings, powder coatings are formulated with crystalline polymers to improve storage stability, reduce melt viscosity, and fluidity and leveling of transparent coatings great influence. Driven by strict environmental protection regulations, powder coatings, like other green coatings, have developed rapidly around the world. The strict requirements for coating technology have enabled powder coatings to have many properties that were considered unattainable in the early 1980s. Powder coatings have clearly penetrated into various important application fields and are widely used by the automotive industry. The development of powder coatings for automobiles will make efforts to further improve weather resistance, UV resistance, low-temperature curability, thin film and improve decoration. The pollution of the three wastes to the environment has become a worldwide problem. Among them, the air pollution caused by solvent-based coatings has attracted the attention of various countries, and the restrictions on VOCs in automobile coatings are becoming more and more stringent. The development of low-pollution coatings is an important topic in the 21st century, and powder coatings will be in an important position. With the development of new powder coating products and new technologies, the application fields of powder coatings will continue to expand, and the proportion of powder coatings in industrial coatings will also increase. At the same time, powder coatings will continue to be one of the coatings with the fastest growth rate. .